1. Field of the Invention
The present invention relates to a micro-machined temperature dependent one-shot valve, and to a process for production thereof. More specifically the present invention relates to a temperature dependent one-shot valve having a rupture mechanism, useful as a safety mechanism of a fuel cell, a feed-starting mechanism of a lab-on-a-chips, and a smart micro-pill, or a like mechanism. The present invention relates also to a process for producing the valve by a micro-machine technologies.
2. Description of the Related Art
Since 1980s, various micro-valves are disclosed which are produced by micro-machine technologiess (hereinafter referred to as “micro-machined valves”); (K. W. Oh, and C. H. Ahn: “A review of microvalves”, J. Micromech. Microeng., 16, R13-R39, 2006). According to the disclosures, the micro-machined valves are classified mainly into two groups: passive valves and active valves.
On the other hand, another type of micro-machined valves are known which are designed to function only once, such as one-shot valves. The one-shot valves are useful, for example, as a valve for triggering a mixing reaction in a lab-on-a-chips, and a valve for delivering a medical sample to a smart micro-pill. The one-shot valves, which are constructed as a thermally operated valve, are useful as a safety valve of a fuel cell of a small portable device having a small fuel tank. Such a valve can be applicable as a rupture mechanism for releasing the pressure when the pressure of the fuel cell rises abnormally owing to a temperature rise.
In the present invention, the one-shot valve which is manufactured by a micro-machine technologies and is operated by a temperature rise is defined as a micro-machined temperature dependent one-shot valve.
A micro-machined temperature dependent one-shot valve is disclosed by O. Guerin, L. J. O. Dubochet, J.-F. Zeberli, Ph. Clot, and Ph. Renaud: “Miniature one-shot valve” IEEE MEMS Conference, pp. 425-428, 1998. This one-shot valve opens a obstructed micro-channel by melting of a polyethylene layer. Therefore, the operation temperature of this valve depends on the melting temperature of the polyethylene.
Another micro-machined temperature dependent one-shot valve which utilizes a micro-sphere is disclosed by P. Griss, Anderson H., and G. Stemme: “Expandable Microspheres for the Handling of Liquids”, Lab Chip, 2:pp. 117-120, 2002. In this micro-machined temperature dependent one-shot valve, a micro-sphere held in a channel expands at or above a preset temperature to a volume of about 60 times the original volume to obstruct the channel. This micro-machined temperature dependent one-shot valve serves to obstruct an release channel.
A still another micro-machined one-shot valve which is operated by an electric current is disclosed by J. T. Santini, A. C. Richards, R. Scheidt, M. J. Cima, and R. Langer: “Microchips as Controlled Drug-Delivery Devices”, Angew. Chem. Int. Ed. 39, pp. 2396-2407, 2000. This valve is placed in a cell in a silicon wafer. At the top of the cell, a metal layer serving as an anode is deposited, and beside the cell another metal layer serving as a cathode is fusion bonded. This valve is immersed in an electrolyte solution. Application of a potential between the anode and the cathode oxidizes the anode and dissolves the anode in the electrolyte solution to open the valve.
Further, a thermal operation valve is disclosed in U.S. Pat. No. 4,313,453. This valve is constituted of a sealing member composed of a solder placed at a metal tube connection portion. This solder stops the flow in the tube. Application of heat melts the solder to open the valve to allow the liquid to flow through the metal tube.
A safety device which prevents a damage of an atomic reactor pressure vessel is disclosed in U.S. Pat. No. 5,526,385. This device has a solder sealing at a pressure-compensation opening. In the normal operation, the solder in a solid state seals the opening: an abnormally high temperature melts the solder and the overpressure inside the reactor pushes out the melted solder to release the pressure.
The above-mentioned disclosed valves have disadvantages as below.
The one disclosed by O. Guerin et al. has its operation temperature not adjustable for its use, although the operation temperature of the micro-machined temperature dependent one-shot valve is preferably adjustable arbitrarily to be suitable for the use. The desired operation temperature of the valve depends on the boiling point of the liquid to be handled, the maximum pressure of the gas in the container, and so forth.
For a pressure release, the stop valve should be capable of opening a flow path. However, the one disclosed by P. Griss et al. serves only to obstruct the flow path, but cannot release the flow path.
The one disclosed by J. T. Santini et al. is useful only in an electrolyte environment, although the valve is preferably useful in any use environment as a safety mechanism or a feed-starting mechanism.
The micro-machined temperature dependent one-shot shot valve can be incorporated in a small system. Further it has advantages below. One advantage is a high responsiveness to the environmental temperature owing to rapid temperature diffusion in its small size of the valve. Another advantage is that the plural devices can be produced in a batch process on one and the same supporting member by a micro-machine technologies, especially an MEMS technique. This enables reduction of the production cost, and enables also simultaneous preparation of a control mechanism like a heater near the valve.
However, the one disclosed in U.S. Pat. Nos. 4,313,453 and 5,526,385 employing a solder is produced necessarily by a typical macro-technique. Therefore the device cannot be made smaller in the size than 2-3 mm3, and the device cannot be produced by a batch process. Further, the control system like a heater cannot be incorporated directly.
The problems with the micro-machined temperature dependent one-shot valve are summarized as below.
At the ambient temperature higher than the preset temperature Tm, the pressure of the pressurized gas or liquid should be released. That is, the valve is designed such that the valve connected to a tank containing a pressurized gas or liquid is kept obstructed below the preset temperature, and opens at a temperature higher than the preset temperature. The temperature Tm of the valve opening should be made readily adjustable in design of the system. The valve should keep obstructing against a large pressure difference at a temperature below Tm in a designed range without leakage.
The valve is useful both in a liquid environment and in a gas environment. Further, the valve is preferably formed in a size typically smaller than 2-3 mm3. The valve is preferably produced by a batch process. The valve can preferably be combined with a heater in the system for on-demand triggering of the valve.